Automatically self-leveling gripping device suspended from the hoisting ropes of a crane

ABSTRACT

A GRIPPING DEVICE IS SUSPENDED FROM THE HOISTING ROPES OF A CRANE AND THE DEVICE IS COMPOSED OF TWO PARTS ONE ABOVE THE OTHER, THE LOWER PART BEING SUSPENDED FROM A CARRIAGE WITH TWO AXLES, WHICH ARE IN TURN SUSPENDED BY PIVOTED ARMS FROM THE UPPER PART. THE LOWER PART IN ITS SUSPENSION BY THE CARRIAGE IS MOVABLE BY AN ACTUATING DEVICE IN A HORIZONTAL DIRECTION WITH REFERENCE TO THE UPPER PART. THE WHEELS OF THE CARRIAGE ARE JOURNALLED ON THE AXLES ECCENTRICALLY WITH RESPECT TO THE BEARING CARRYING THE PIVOTED ARMS AND ON EITHER AXLE THERE IS INTEGRALLY FIXED A PROTRUDING ARM, THE ENDS OF WHICH ARMS COOPERATE WITH LIMIT SWITCHES FOR STARTING OR STOPPING THE ACTUATING DEVICE.

Jan. 1971 KEIJO'LEHTONEN 3,552,793

' AUTOMATICALLY SELF-LEVELING GRIPPING DEVICE SUSPENDED FROM THE HOISTING ROPES OF A CRANE Filed May 10. 1968 United States Patent lice 99/ Int. Cl. B66c 1/00 U.S. 'Cl. 294 67 5 Claims ABSTRACT OF THE DISCLOSURE A gripping device is suspended from the hoisting ropes of a crane and the device is composed of two parts one above the other, the lower part being suspended from a carriage with two axles, which are in turn suspended by pivoted arms from the upper part. The lower part in its suspension by the carriage is movable by an actuating device in a horizontal direction with reference to the upper part. The wheels of the carriage are journalled on the axles eccentrically with respect to the bearing carrying the pivoted arms and on either axle there is integrally fixed a protruding arm, the ends of which arms cooperate with limit switches for starting or stopping the actuating device.

' The largest standard length of a container in 40 ft. When such a long container is filled with goods, the center of gravity of the container does not always conside with the geometric center, or centroid; the center of gravity may deviate considerably from the point mentioned. When subsequently the gripping element'of the crane seizes the container at.the-'center and the container is raised from its supporting base, it naturally assumes an inclined position. This subjects'the'goods in the container and their fixing elements .to great stress. The goods may come loose, they may be disarranged and they may slide towards the lower end' of the" container, whereby the center of gravity is still further displaced towards one end of the container.

It is obvious that an inclined position of the container suspended from the gripping element of the crane cannot be permitted because the goods in the container might be damaged. On the other hand great difficulties are encountered in depositing a container hanging in inclined position, for example, into a ships hold, and this is sometimes impossible; For this reason gripping elements have been developed by means of which the container may be seized so that the hoisting point is located vertically over the center of gravity, whereby the container suspended from the gripping element thus is maintained in horizontal position.

A gripping element is known which is composed of two parts located one above the other, with the lower part suspended from a carriage with two axles which have been suspended from the upper part by pivoted arms, and whereby the lower part in suspension by the carriage can be moved with the aid of an actuating device in a horizontal direction with reference to the upper part. The actuating device may consist of a hydraulic cylinder or of a mechanical device, screw, tooth rack, etc. operated by an electric motor.

When the person operating the crane makes this known gripping element engage the container and when he starts the hoisting, he will notice at once whether the container rises in horizontal or inclined position. If the container tends to rise in inclined position, he lowers it back to the supporting base and displaces the upper and lower parts of the gripping element horizontally with respect to each other so that the hoisting point and the center of gravity come closer together. If on subsequent hoisting the container still assumes an inclined position, another correction is performed.

This procedure obviously consumes time and reduces the capacity of the crane. An object of the present invention is to provide a device which immediately and automatically on raising the container displaces the upper and lower parts of the gripping element horizontally with respect to each other so that the hoisting point and the center of gravity of the container come to be on the same vertical line. The invention is characterized in that the wheels of the carriage in the gripping element have been journalled on axles eccentrically with reference to the bearings supporting the pivoted arms and that to either axle a protruding arm has been integrally fixed, the ends of these arms cooperating with limit switches which start or stop the said actuating device.

When the container is raised, a moment is produced on both axles of the carriage for the reason that the center of the carriage wheels and the center of the bearings of the pivoted arms do not coincide. These moments tend to rotate the axles and, as a consequence, also the protruding arms integrally fixed to the axles. If the center of gravity of the container and the hoisting point are located vertically above each other, the moments tending to turn the axles of the carriage are equal but opposed and they cancel each other. But if the center of gravity and the hoisting point are not on the same vertical, the axles of the carriage and thus also the protruding arms integrally fixed to them will be turned, whereby the ends of these arms act on the limit switches, which start the actuating device so that the lower part of the gripping element and consequently also the center of gravity is displaced in horizontal direction with reference to the upper part. When the center of gravity has reached the position vertically under the hoisting point, the moments acting on the axles become equal and opposite so that they cancel each other, at which the arms protruding from the axles by means of the limit switches stop the actuating device.

The invention is described for illustration in the following with reference to the attached drawing, where:

FIG. 1 schematically illustrates the gripping element in elevation view, and partly in section, FI151G. 2 is a sectional view along the line II-'II in The gripping element comprises upper part 1 and lower part 2. The upper part 1 is suspended from hoisting ropes, which have been indicated by arrows 3. The lower part 2 is suspended from the upper part 1 by pivoted arms 4. The lower ends of these pivoted arms are journalled on the axles 6 of a carriage 5 each with two wheels 7. For the wheels 7 of the carriage a track 8 is provided on the lower part 2 of the gripping element. The ends of the lower part 2 of the gripping element have not been shown in the drawing because they have no significance in the present invention.

The wheels 7 of the carriage 5 and the bearings 9 supporting the pivoted arms 4 are carried on the axle 6 eccentrically with reference to each other. In FIGS. 1 and 2 the dash-dot line 10 indicates the centerline of the wheel 7 and the dash-dot line 11, the centerline of the support bearing 9. At the middle of the axle 6 a protruding arm 12 is fixed with a key and which is directed toward the opposite end of the carriage. The end of this arm 12 rests on one arm of a two-armed lever 13- carried in bearings in the lower part 2 of the gripping element. On the opposite arm 14 of the two-armed lever rests an arm 15 similarly fixed to the other axle of the carriage 5. Both arms 13, 14 of the lever are loaded by springs 16, 17. On the body of the carriage 5 above the two-armed lever 1}, 14 two limit switches 18, 19 are fixed, their pushers being located immediately above the lever arms 13, 11'

center of gravity of which coincides with its mathematical center. In other words, the center of gravity is located under the hoisting point, or the center of the hoisting ropes 3. When the container is now lifted oif its base, load is applied to the axles 6 of the carriage 5, and the moment due to eccentricity tends to rotate the axles 6. The moments acting on both axles are equal in magnitude and opposite in direction. No rotation of the axles 6 occurs because the arms 12 and 15 fixed to them act with equal force on the opposite arms of the lever 13, 14, whereby the forces cancel each other. i

If, on the other hand, the center of gravity of the container is closer to one of its ends, the axles 6 are loaded byforces different in magnitude, whereby also the moments tending to turn them diifer in magnitude. Both axles are then rotated in the direction determined by the greater of the two moments. At the same time the arms 12 and 15 fixed to the axles 6 are turned. These arms in their turn cause the two-armed lever 13, 14 to turn. Assuming that the lever is turned in clockwise direction in FIG. 1. The lever arm 13 then depresses the pusher of limit switch 18. This limit switch in its turn opens a pressure mediumgoverning valve (not depicted) so that a double-acting pressure cylinder 20 begins to operate. The piston rod21 of the cylinder 20, which has been attached to the body of the carriage 5 by means of the lug 22, now moves the carriage 5 towards the equilibrium position. When the equilibrium position has been reached, the axles 6 and together with them the arms 12 and 15 turn back into their initial position, whereby the limit switch 18 closes the valve governing the pressure medium.

It is obvious that the center of gravity of the container need not be exactly under the hoisting point. The container remains horizontal even if there should be slight deviations. The springs 16 and 17 serve the purpose of counteracting the tendency of the lever 13, 14 to turn in order that the device according to the invention might not be unnecessarily sensitive and respond by corrective action to minimal deviations of the center of gravity.

Embodiments of the invention may naturally vary within the scope of the invention. For instace, it is obvious to one skilled in the art that the wheels 7 of the carriage 5 may be replaced with sliding shoes journalled on the axles 6. Likewise, it is possible to use an electric motor as an actuating device, in lieu of pressure cylinder 20.

I claim:

I. 'A"'g'ri'ppingdevice adapted for Being-srrspende-crfrom hoisting ropes of a crane ;,to engage a container, said gripping device comprising first and second parts located one above the other, a pair of arms pivotably connected to,the upper parta carriage including two spacedfixles, hearings on said axles suspending said carriage from aid arms, support means on said carriage -forsuspending the lower part from vthe carriage and enabling 'relative displacement therebetween, act'uatormeans for providing relative horizontal displacement between tl 1e*1ower part and the upper part, said support means being supported on said axles eccentrically .with .respect to said bearings such that if the center of gravityof the lower part and any load thereon is not centrally disposed between the afxles, the axles will undergo'rotation, and means coupled to said axles for sensing rotation of said axles to activate the actuator means to centrally locate the cente'fof gravity between the axles. F

2. A device as claimed in claim- 1,"whe'rein said-support means comprises wheels.

3. A device as claimed in-claim 1, wherein said means for sensing rotation of the axles to activate-the" actuator means comprises a protruding arm fixedon each axle, and'switch means operatively positioned with respect to each arm to control the opeation of the 'actilatonmeans.

4. A device as claimed in claim 3,"wherein the protruding arms of the axles extend towards each other, said means for sensing-rotation of the axles further comprising a two arm lever pivotably connected to' said lower part, each arm of said lever facing a respective protruding arm and a respective switch means.

5. A device as claimed in claim 4, wherein said means for sensing rotation of the axles comprises spring means acting on each arm of said two arm lever to resist rotat on of the lever under the action of said protruding arms.

:References Cited UNITED STATES PATENTS H 3,433,459 3/1969 Logan 21.2;1 4X

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